Reaction of 3,4,5,6-tetrahydro-2-pyrimidinethiol, prepared by cyclocondensation reaction of 1,3-diamino propane 1 and carbon disulfide, with ethyl chloroacetate and substituted aromatic aldehydes in the presence of sodium acetate and acetic acid gave 2-[(Z)-1-(aryl)]-6,7-dihydro-2H-isothiazolo[2,3-a]pyrimidine-3(5H)-one derivatives 3(a-j) in good yields. 1H-NMR spectroscopy, and elemental analysis were used for identification of these compounds.